Why is this guys mini lathe parting off so well?

The trick to parting-off is to get the chips out of the groove so they don't pile up and cause a jam. Use whatever means available to do that and parting becomes less of a scare. I think the 'be brave with the infeed' advice works because it usually results in long swarf being created that naturally clears from the slot.

Martin.

Hi Philip I made a rear part off toolpost and I have never looked back. I found that the slightest wobble from the toolpost on compound slide ended in catastrophe and risked damaging the lathe so I made a rear toolpost and mounted it on the top slide direct. It is upside down so I don't have to reverse the spindle and any swarf drops out. It is also always on center height and dosnt need adjusting.

David

I think one of the failings of the small mini lathes is the lack of rigidity of the tool mount/compound slide through to the cross slide, you can see in the video the amount of flex at the tool post.

My CJ18 mini lathe was a bit of a nightmare when parting off, it depended on the job it was sort of ok with not too heavy or deep cuts in aluminium but parting steel was always a problem.

I went down the rear tool post route which transformed it and made parting off a pleasure to do, it did mean however making a heavier duty cast iron cross slide with T slots and a 50mm square steel tool post for the parting tool. Obviously a fairly serious mod but it did cure the parting problems and to some degree improved general turning having a heavier cross slide bed.

Picture below of the original cross slide and the heavier version, not a 5 minute mod but it was worth the effort.

Ron

Edited By Ron Laden on 22/10/2020 14:20:20

Note to oneself. Make a rear holder for parting off. Something i have been meaning to do for some time. Always good reports from those who use that method.

Steve.

Whether or not a rear toolpost is worth making or obtaining depends on how much parting-off you really need to do and how much of a fetish you're prepared to make of it. If you're making several tens of something from bar stock it's worth having and may even be worth making.

If you generally part-off half-a-dozen or so times a week, and you have to do your milling in the lathe for the time being, the location is better used for a vertical slide - and you resolve your parting problems well enough so they don't get in the way of what you want to do.

There can be problem materials for parting, but with those you usually find that parting's only another aspect of the misery you'll meet in other kinds of op too.

If the tool's sharp, square to the spindle axis, on-centre, as close as practical to the chuck, and the right width and protrusion for the work, it shouldn't be so stressed as to nod the toolpost or flex the compound, even in a tiny lathe. Those movements in the vid were a clear sign that other things were wrong.

For the record youtu.be is a URL registered in Belgium and used to generate shortened versions of YouTube links by their system.

Neil

For the record, from the Be (Belgium) DNS:

Posted by Vic on 22/10/2020 11:05:02:

I've seen these mentioned, why are they not more popular?

I bought some steel from the local stockholders as it was dirt cheap. I've just looked up the EN1A steel, though one problem will be that it can't be zinc plated once machined due to the lead content (according to Google).

Did you make the new cross slide? Does it also use gibs with bolts to tighten it up?

This is the parting tool that Arc recommended: https://www.arceurotrade.co.uk/Catalogue/Cutting-Tools/Lathe-Turning-Tools/8mm-Parting-Off-Tool-with-Parting-Blade

Thank you for all the friendly replies. I can't answer every post but will be trying out all the tips and advice and I'll let you know what happens.

As another fairly inexperienced mini lathe owner, I'd say don't rush into changing things (especially spindle bearings) - there may well be bigger improvements to be made through set-up and technique.

In addition to all the advice above, I'd say to run the spindle as slowly as you sensibly can (maybe 150RPM or less), at least to start with. My lathe has a brushless motor (no high/low gear) which might make this easier.

Check your compound slide for play (grab the toolpost and rock it across the direction of slide travel and look closely at the joint between the two halves of the slide for signs of movement.

[The main issue with my compound slide was that the gib strip was rocking as load came on the toolpost, allowing the slide to lift. The problem (in my case, and I suspect many others) was that the gib adjustment screws were acting too far back from the sliding face of the gib for it to be stable (the gib is too thick for its height). This was compounded by the shape of the adjusting screw tips and recesses in the gib.]

Bolt the lathe down to something (with care to avoid distorting it) - this helped a lot with mine - see here

Edited By Andy Gray 3 on 22/10/2020 20:12:33

Edited By Andy Gray 3 on 22/10/2020 20:13:31

I have something very similar, and don't find it very useful - I do use it on a quick change toolpost for small diameter brass / ali or for cutting grooves.

I found this type much less touchy and more useful:

https://www.rdgtools.co.uk/acatalog/SMALL-PRO-PARTING-SYSTEM--9MM-SHANK--1729.html

I havent got the Arc Euro one but it's important to check that the blade is being held properly upright with this type of holder. If it's leaning over by just a few degrees that will mean that the clearance angle on one side is not doing its job and that side can rub. I needed to use some shim to make sure my blade was properly vertical.

You can also check this by trying to lift the topslide from underneath the dial end - you may find an alarming amount of play.

On my mini-lathe this was due to the cross slide gib being completely the wrong shape in cross section, and not deep enough to fill the space in which it was supposed to work. I made a new one from brass - quite fiddly due to the difficulty of actually gripping the thing - if you're a beginner, you might want to leave doing this for a while.

To be getting on with, if your gib strip is like this I reckon you could probably make it work a lot better by shimming it against the underside of the cross slide - an old beer can is a useful source of aluminium shims. Try to fill the gap at the top as much as possible short of making it jam.

Philip, yes I did make the heavier duty cross slide but like I said it is quite a serious mod, picture below of finished item. You need a sizeable chunk of cast iron, a T slot cutter and a dove tail cutter, and a mill. Yes the cross slide is gib mounted with adjusting screws but I increased the screws from 3 to 5.

Before getting in to any serious mods and I am not suggesting for one minute that you make a new cross slide, I did but I wanted a rear tool post and T slots. Have you tried inverting the parting tool and running the lathe in reverse, quite a few people seem to get better results in parting this way on the mini lathe.

I was asking more out of curiosity, that is too much of a mod for me, though I'll consider the rear toolpost for a later date.

I just shimmed the gibs on the underside of the carriage as they were riding on the edge of the ways. I used shim washers instead of cutting strips of shim that most people use, seems rigid. Fitted the Arceurotrade brass gibs; one has made an improvement, letting me tighten up the gib more while still letting the side move. But the other gib is the wrong size and just jams the movement.

I'll probably fit the taper bearings as I have them now, but need to make a special nut to hold the back of the main shaft for the puller. That's a 30mm part so will see if I can part that off or if I have to resort to a hacksaw.

I personally use an arc 3/32 parting blade and it's fine on my Chester DB7....as long as it's sharp, and set at the correct height. I tried with 1/16, and it was too flexible - it wondered off easily, even on brass.

Here is my version for a parting tool. The cutting tool is in compression, avoiding the flexure due to the conventional cantilevered parting tool

https://www.youtube.com/watch?v=S8HvS13L7MU

Alan